Postprandial glycemia (PPG) predicts morbidity and mortality and is a therapeutic target for patients with type 2 diabetes (T2D). Mixed meal tolerance tests (MMTT) consisting of carbohydrate, protein, and fat are rarely used to evaluate PPG but mirror macronutrient consumption in the living condition and have practical validity. PURPOSE: This study aimed to compare the gluco-metabolic responses (glucose, insulin, and c-peptide concentrations) to a mixed meal following 7 days of aerobic exercise in sedentary participants with T2D to evaluate changes in PPG and its regulation in response to daily exercise. METHODS: Sedentary (exercise <2x/wk), older (48-67 yrs), overweight to obese (BMI 25.0-37.0 kg/m2) women and men (n=10) with T2D completed baseline measures, including a maximal exercise treadmill test, prior to pre- and post- intervention (PRE; POST) testing. For three days before PRE or POST testing, participants consumed a control diet provided by our metabolic kitchen with 60% energy as carbohydrate, 30% fat, and 10% protein. On day four, participants arrived fasted for a MMTT, and a catheter was inserted into the forearm for collection of arterialized venous blood using a heated box. Blood samples were taken before the meal and over a 240 minute time course after meal consumption (400 kcal breakfast wrap and orange juice; same composition as control diet). The intervention consisted of supervised 60 minute aerobic exercise sessions (60-65% heart rate reserve; treadmill walking and stationary cycling) for seven consecutive days. Snacks (~400 kcal) were provided following exercise to promote body weight stability during the intervention period. RESULTS: Incremental area under the curve (iAUC) was not different for circulating glucose PRE and POST, but both circulating insulin iAUC (PRE: 8113 ± 806 µIU·min/mL, POST: 6797 ± 546 µIU·min/mL; p < 0.05) and c-peptide iAUC (PRE: 1197 ± 108 ng·min/mL, POST: 1027 ± 52 ng·min/mL; p < 0.05) were lower after the exercise intervention. CONCLUSION: Lower POST vs. PRE insulin and c-peptide concentrations for the same blood glucose concentration implies that increased insulin sensitivity occurs as an early response to daily exercise, independent of changes in blood glucose levels. Lower c-peptide, in particular, suggests that this may be due to decreased insulin secretion.

ACKNOWLEDGEMENTS: This study was funded by an ACSM pre-doctoral student research award.